(1) Field of the Invention
The present invention relates to a light emission apparatus used as a light source of an illumination apparatus and of a display, and in particular relates to a technology for restricting deterioration in resin materials used in such a light emission apparatus.
(2) Related Art
Recently, in the field of illumination apparatuses, LED is getting attention as a light source. This is because with LED, light emitting energy can be expected to be improved in the future by research and development. Moreover, with LED, a surface light source with high intensity can be obtained by mounting a plurality of LEDs.
An example of surface light source using LEDs is disclosed in “Optical display” Ohm MOOK Hikari series No. 2, Ohmsha Ltd., Feb. 25, 2002, p. 46–52. In this document, a plurality of shell-type white LEDs are arranged on a substrate. Here, the shell-type white LED has a structure of molding LED chips emitting light having comparatively high energy such as blue to violet light (hereinafter, such a light is referred to as “excitation light”), with use of a resin in which phosphor particles that emit red, green, and blue lights by means of the excitation light are mixed (refer to published Japanese translation of a PCT application No. 2000-509912).
Incidentally, the resin generally deteriorates because the atom coupling is cut by means of the energy that the light has. In particular, the excitation light has a high energy, and so the deterioration in resin is prominent.
With the shell-type white LED, its chip has been molded by a resin. The resin is easy to deteriorate by means of the excitation light, and so turns yellow thereby changing light-emitting color, or cracks which then incurs entry of water, thereby deactivating the phosphor particles from the entered water, or increasing leak current in a case where the water adheres to the surface of the LED chips. In addition, the shell-type white LEDs are so-called discrete parts that emit white light independently from one another, therefore have limitation in enhancing mounting density, and incur large cost.
In view of the above problems, it is desired to structure a high-intensity surface light source, without using such a shell-type white LED.
In order to satisfy such a request, a hybrid structure has been considered in which LED chips, in a necessary number, are mounted on the substrate with high density, on which a phosphor film is disposed. By this hybrid structure, the excitation light emitted from all the mounted LED chips is converted into visible light by means of the phosphor film. With this structure, the mounting density of the LED chips is enhanced, while using the existing chip mounting technology. This is advantageous with a view towards easy implementation and cost-effectiveness.
In spite of these advantages, however, the hybrid structure is expected to have a problem that, since all the excitation light emitted from the LED chips will not be converted into visible light by the phosphor film, a part of the excitation light will be reflected on the resin covering the insulating substrate, to deteriorate the resin. Use of a ceramic substrate works to counter this problem. However, because of being expensive, the ceramic substrate is not suitable for this use if it requires numerous chips and so requires a large area. Other means can be also considered, such as reducing the amount of excitation light that is reflected from the phosphor film, or processing the substrate to be light resistant, in particular to be ultraviolet resistant. However, there is a limitation in preventing the excitation light from reflection. In addition, new problems are considered to arise. One example is that a heat emitted from the LED chip will be accumulated thereby deteriorating thermal-dissipation characteristic, in a case where, in an attempt to delay deterioration, a substrate is used that has a thick resin layer as a means to process the substrate to be light resistant. These problems similarly happen for the display in which numerous LED chips are disposed (in this specification, a combination of an illumination apparatus and a display is defined as “light emission apparatus”).